The invention relates to gate valves, and more particularly to knife gate valves with peripheral seals.
In prior art sealing arrangements, seals of the described type are retained in the body in a groove and use a metal reinforcing ring which is encapsulated in the seal. The seal is positioned around the edge of the gate forming a compression seal. These type of seals are retained on three sides in the body and provide bidirection shutoff. Problems with such type prior art sealing systems include the method of retaining the seal and the way a tight seal is affected. The metal reinforcement must be strong enough to retain the seal in the groove yet flexible enough to thread around the body. In some applications these seals have been sucked out of the valve. Since sealing is affected by compression of rubber between the gate edge and the body, the modulus for a compressive system limits the strain linearity to about 30%. Compression set becomes a limiting factor which causes a premature loss of sealability and leakage.
U.S. Pat. Nos. 4,679,770 (Liberman), 4,206,905 (Dobler), and 4,703,915 (King) describe U-shaped seals on the periphery of the gate, but do not describe a retention arrangement or shear loading according to the invention. U.S. Pat. No. 4,377,274 (Mayhew, Jr.) describes a knife gate valve with flat rigid frame. U.S. Pat. Nos. 2,462,493 (Hamer) and 2,851,051 (Englert et al.) show trapezoidal slots for retain seal elements; U.S. Pat. No. 2,873,943 (Williams) describes a valve with a removable seat; U.S. Pat. No. 3,353,832 (Coulson) describes a trapezoidal seal with a wire rod support; a drum seal arrangement is shown in U.S. Pat. No. 863,001; and other gate valve seal arrangements are shown in U.S. Pat. Nos. 2,893,684 (Williams et al.); 3,223,381 (Fischer, et al.); 4,522,224 (Stalder et al.); 4,623,122 (Gambetta).
Accordingly, the limitations of the prior art arrangements are overcome by the novel arrangement for retaining and loading the seal according to the invention.